Reactive flow agent for powder coatings

ABSTRACT

The present invention relates to a thermoset powder coating composition and method of application. The coating includes a copolymer having a reactive functionality selected from the group consisting of epoxy, carboxy, and hydroxy functionalities and mixtures thereof, a suitable crosslinking agent capable of reaction with the reactive functionality on the copolymer, and an aliphatic or aromatic crystalline, hydroxyl containing compound having a melting point of between 30° C. and 150° C. and a flow control agent. The powder coating is a pigmented or clear coat powder composition applied over a primer layer.

FIELD OF THE INVENTION

The present invention relates to thermosetting powder coatings and tomethods for coating substrates with the powder coating compositions.More particularly, the invention relates to the use of reactive flowagents in thermosetting powder coatings and to methods for coatingsubstrates with these powder coatings.

BACKGROUND OF THE INVENTION

Powder coating compositions are advantageous as they have very lowvolatile organic content and give off very little volatile material tothe environment when cured.

In the preparation of powder coatings problems are often encountered inflow and leveling. Flow is the resistance to movement by a liquidmaterial. Leveling is the measure of the ability of a coating to flowout after application so as to obliterate any surface irregularitiessuch as orange peel, peaks or craters produced by the mechanical processof applying or coating. Often when flow and leveling are improved,application characteristics such as sprayability, fluidization andimpact fusion are affected detrimentally. The present invention isdirected to improving flow and leveling without adversely affectingapplication characteristics.

SUMMARY OF THE INVENTION

The present invention relates to the use of a hydroxyl containingaliphatic or aromatic crystalline compound, having a melting pointbetween 30° C. and 150° C. as a flow control agent in conjunction withconventional flow control agents in thermoset powder coatingcompositions. The powder coating is a pigmented or clear coat powdercomposition and is preferably applied over cured electrocoat. Thecoating composition includes a polymeric resin comprising a copolymerhaving a reactive functionality selected from the group consisting ofepoxy, carboxy, and hydroxy functionalities and mixtures thereof, and asuitable crosslinking agent capable of reaction with the reactivefunctionality on the copolymer.

The present invention also provides a method of coating a metalsubstrate with the coating composition comprising the steps of a)electrodepositing a primer layer on the surface of the metal substrateand b) applying a thermosetting layer of the powder coating compositiondescribed above over the previously applied electrodeposited primerlayer and c) curing both layers either simultaneously or curing theelectrodeposited layer before application of the thermosetting layer andthen curing the thermosetting layer.

The use of the aliphatic or aromatic crystalline compound describedabove, in combination with one or more additional flow agents in apowder coating composition reduces the viscosity of the overall systemand aids in coalescing the film. The resulting cured film demonstrates amarked reduction in orange peel formation and consequently, improvedfilm smoothness.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to the use of a hydroxyl containingaliphatic or aromatic crystalline compound having a melting pointbetween 30° C. and 150° C., as a flow control and leveling agent inconjunction with conventional flow control agents for use in thermosetpowder coating compositions. Examples of suitable crystalline compoundsinclude trimethylolpropane (TMP), neopentyl glycol, 2,5dimethyl-2,5-hexanediol, 2,4,6-triphenylphenol, 2, 2' biphenol,9-phenanthrol and p-cresol. The crystalline compound is used in amountsbetween 0.05 and 10.0 % by weight, based on the total coatingcomposition weight, preferably in amounts between 0.5% and 5.0 % byweight based on total coating composition weight. The crystallinecompound is useful in thermoset powder coatings including a copolymerhaving one or more reactive functionalities and a crosslinking agentcapable of reacting with the reactive functionality on the copolymer.

Polymeric resins useful for the present invention include polyester,acrylic and epoxy resins. Useful polyester resins are obtained bycondensation polymerization reaction between a saturated poly-basic acidor its anhydride and a polyalcohol. Examples of dibasic acids and acidanhydrides for this purpose include phthalic acid, phthalic anhydride,isophthalic acid, terephthalic acid, hexahydrophthalic anhydride,tetrachlorophthalic anhydride, hexahydrophthalic anhydride, pyromelliticanhydride, succinic acid and adipic acid. Examples of useful polyols areethylene glycol, diethylene glycol, triethylene glycol, propyleneglycol, dipropylene glycol, glycerin, trimethylolpropane,pentaerythritol, neopentyl glycol and hydrogenated bisphenol A.

Crosslinking agents for the polyester resins include acid anhydrides,such as pyromellitic anhydride, trimellitic anhydride, phthalicanhydride, and succinic anhydride; aminoplasts such ashexamethoxymethylolmelamine, trimethylolmelamine trimethyl ether,hexamethylolmelamine hexamethyl ether, hexamethylolmelamine andtrimethylolbenzoguanamine; glycol urils; and blocked aliphatic andaromatic diisocyanates, such as blocked hexamethylene diisocyanate,blocked isophorone diisocyanate and blocked polymethylenepolyphenyl-isocyanate.

Examples of epoxy resins include bisphenol A type epoxy resin, a novolacepoxy resin or an alicyclic epoxy resin. Crosslinking agents for theepoxy resins include dicycandiamide and its derivatives; acid anhydridessuch as phthalic anhydride, trimellitic anhydride, pyromelliticanhydride, hexahydrophthalic anhydride, maleic anhydride and succinicanhydride; aromatic diamines such as ethylenediamine,metaphenylenediamine, 4-4'-diaminodiphenylmethane, 4,4'-diamino-diphenylsulfone and 4,4'-diamino-diphenyl ether; imidazole and dihydrazide.

Examples of suitable acrylic polymers for purposes of the presentinvention are well known in the art, and can be prepared by polymerizingcopolymerizable monomers with other functional group-containingmonomers. Suitable copolymerizable monomers include olefinic unsaturatedmonomers such as ethylene, propylene and isobutylene, aromatic monomerssuch as styrene, vinyltoluene and α-methyl styrene, esters of acrylicacid and methacrylic acid with alcohols having 1 to 18 carbon atoms suchas methyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate,n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate,cyclohexyl acrylate, cyclohexyl methacrylate, 2-ethylhexyl acrylate,2-ethylhexyl methacrylate, lauryl acrylate and lauryl methacrylate,vinyl esters of carboxylic acids having 2 to 11 carbon atoms such asvinyl acetate, vinyl propionate and vinyl 2-ethylhexylacrylate and otherco-monomers such as vinyl chloride, acrylonitrile and methacrylonitrile.These co-monomers can be used singly or as a mixture of two or more ofthem. Suitable functional group containing monomers are described asfollows.

For example, hydroxy-functional acrylic polymers are formed by reactionof the copolymerizable monomer with hydroxyethyl acrylate, hydroxybutylacrylate, hydroxybutyl methacrylate, hydroxypropyl acrylate and thelike. Amino functional acrylic monomers would include t-butylaminoethylmethacrylate and t-butylaminoethylacrylate. For purposes of the presentinvention, preferred hydroxy functional acrylic resins have a molecularweight of between 10,000 and 50,000.

Epoxy functional groups are incorporated into the acrylic polymer byreaction with monomers having epoxy functional groups such as glycidylacrylate, glycidyl methacrylate, allyl glycidyl ether.

Carboxy functional groups are incorporated into the acrylic polymer byreaction with acrylic acid, methacrylic acid, itaconic acid, maleicacid, fumaric acid, and monoesters of maleic acid and fumaric acid withmonohydric alcohols.

For purposes of the present invention, hydroxy functional acrylic resinsare crosslinked by the aminoplasts described above as useful forpolyesters. Other useful crosslinkers include blocked diisocyanates,formed by reacting a blocking agent with diisocyanates includingisophorone diisocyanate, the isocyanurate of hexamethylene diisocyanate,toluene diisocyanate, methylene diphenyl diisocyanate, methylenedicyclohexyl diisocyante, 2-methyl-1,5-pentane diisocyanate,2,2,4-trimethyl-l,6-hexane diisocyante and 1,12-dodecane diisocyanate.

Preferable blocking agents for reaction with the diisocyanates areoximes, such as methylethyl ketoxime, methyl-n-amyl ketoxime, acetoneoxime, cyclohexanone oxime and caprolactam. Other blocking agentsinclude malonic esters and any suitable aliphatic, cycloaliphatic,aromatic and alkyl monoalcohols. Additional blocking agents include thelower aliphatic alcohols such as methyl, ethyl, chloroethyl, propyl,butyl, amyl, hexyl, heptyl, octyl, nonyl, 3,3,5-trimethylhexanol, decyland lauryl alcohols, and the like. Examples of aromatic-alkyl alcohols,include phenylcarbinol, ethylene glycol monoethyl ether, monobutylether, monopropyl ether and the like. Other blocking agents are phenoliccompounds such as phenol itself and substituted phenols where thesubstituents do not adversely affect the coating operations includingcresol, nitrophenol, chlorophenol and t-butyl phenol. Also suitable aredibutyl amine and tertiary hydroxyl amines such as diethylethanolamine.

The blocked diisocyanate crosslinkers of the present invention areformed by reacting sufficient quantities of organic polyisocyanates,with sufficient quantities of blocking agent, at a sufficienttemperature, for a sufficient amount of time, under reaction conditionsconventional in the art, such that no free isocyanate groups are presentwhen the reaction has run its course.

Generally, the blocked crosslinkers are available commercially.Preferred crosslinkers for purposes of the present invention include theblocked isocyanurate of isophorone diisocyanate, available as and theblocked isocyanurate of hexamethylene diisocyanate.

Where the functional radicals of the resin are carboxyl, thecross-linking agent may be selected from the group consisting ofdi-epoxy compounds, polyoxazolines and polydioxanes.

Where the functional radicals of the resin are glycidyl, examples ofsuitable crosslinking agents are polycarboxylic acids and theiranhydrides such as phthalic acid, phthalic anhydride, trimelliticanhydride and pyromellitic anhydride; polyphenols such as catecol,resorcinol, hydroquinone, pyrogallol and fluoroglumine; and polyaminessuch as ethylenediamine, metaphenylenediamine,4-4'-diaminodiphenylmethane, 4,4'-diamino-diphenyl sulfone and4,4'-diamino-diphenyl ether.

The polymeric resin is utilized in an amount between 90 and 10% byweight, and preferably in an amount between 60 and 20% by weight, basedon total coating composition weight. The crosslinking agent is utilizedin amounts between 10 and 90% by weight, and preferably in amountsbetween 20 and 50% by weight, based on total coating composition weight.

In addition to the polymeric resin and crosslinking agent, additivesincluding pigments, fillers, thickeners, plasticizers, flow additives,hindered amine light stabilizers and ultraviolet light absorbers mayalso be added.

Pigments are utilized in amounts between 0 and 35% by weight, based ontotal coating composition weight. Other additives comprise between 5 to30%, preferably 10 to 25% by weight, based on total coating compositionweight.

The thermosetting powder coating compositions can be prepared by meltblending the ingredients of the coating compositions. This can beaccomplished by first dry blending the ingredients in a planetary mixerand then melt blending the admixture in an extruder at a suitabletemperature within the range of from 80° C. to 130° C. The extrudate isthen cooled and pulverized into a particulate blend.

The thermosetting powder coating composition can then be applieddirectly to a substrate of, e.g., a metal such as steel or aluminum.Non-metallic substrates such as plastics and composites can also beused. Application can be by electrostatic spraying or by use of afluidized bed. Electrostatic spraying is the preferred method. Thecoating powder can be applied in a single sweep or in several passes toprovide a film thickness after cure of from 1.0 to 8 mils.

The substrate can optionally be preheated prior to application of apowder coating composition to promote uniform and thicker powderdeposition.

A pigmented powder primer-surfacer composition can be applied directlyupon bare metal, e.g., upon untreated, unprimed steel, or uponpretreated, i.e., phosphatized unprimed steel. The primer-surfacercoating compositions can also be applied upon phosphatized steel havinga thin (1.0 to 2.0 mil) layer of an electrodeposited primer, cured oruncured before the application of the powder coating compositions. Inthe preferred embodiment, the primer-surfacer is applied over a curedelectrodeposited primer coating upon the metal substrate. Afterapplication of the powder primer-surfacer, the panels were baked forbetween 20 and 90 minutes at between 162° and 191° C.

Alternatively, the powder coating composition can be applied directlyupon an uncured electrodeposited primer coating and the powder coatinglayer can be co-cured by heating at temperatures between 149° C. and177° C. for from 10 minutes to 90 minutes.

A non-pigmented powder coating prepared according to the presentinvention can be applied over the coatings described above. Wheredesired, applications of basecoat and clearcoat are made and baked forbetween 25 and 45 minutes at temperatures between 121° and 135° C.

The powder coating compositions of this invention exhibit improved flowcharacteristics compared to conventional powder coating compositions. Inaddition, the powder coating compositions of the invention haveexcellent stability and impact resistance.

After application and curing of the powder coating composition, at leastone topcoat layer is applied over the coating layer. The topcoat can be,for example, a polyester-based coating cured with an aminoplast resin,an acrylic polymer-based coating cured with an aminoplast resin, a mixedresinous blend of an acrylic polymer and polyester containing coatingcured with an aminoplast resin. The topcoat may be solvent-based,water-based or a powder coating. The topcoat layer may be a compositecoating comprising a colored or pigmented basecoat over which isdeposited a transparent or clear coat.

The invention is further illustrated by the following examples.

EXAMPLES Examples 1-9 Primer-surfacer Powder Coatings

Powder coating compositions were prepared from the ingredients set forthin Table 1 below. The powder coatings were prepared by premixing theingredients for 30-90 seconds, until homogenous. The premixed blend wasthen extruded on a ZSK-30 (Werner Pfleider) twin screw extruder at thefollowing conditions.

Zone 1=130° C.

Zone 2=130° C.

RPM=250

The flake was re-extruded at the above conditions. The flake was thenground on an ACM-2L mill to 22-25 microns.

Coatings were applied with an ONODA spray gun, Model No. GX108. Panelswere sprayed with the powder coating composition to a thickness ofbetween 1.0 and 8 mils over electrocoated cold rolled steel (CRS). Thepanels were baked for 30 minutes at 350° F.

Example 10 Clearcoat Powder Coating

The clearcoat powder coating is prepared by premixing the ingredientsfor 30-90 seconds, until homogenous. The premixed blend is then extrudedon a ZSK-30 (Werner Pfleider) twin screw extruder at the followingconditions.

Zone 1=130° C.

Zone 2=130° C.

RPM=250

The flake is then re-extruded at the above conditions. The flake is thenground on an ACM-2L mill to 22-25 microns.

Coatings are applied with an ONODA spray gun, Model No. GX108, to panelsat a thickness of between 1.0 and 8 mils over electrocoated cold rolledsteel (CRS). The panels are then baked for 30 minutes at 350° F.

                                      TABLE 1                                     __________________________________________________________________________    EXAMPLES 1-10                                                                            EXAMPLES                                                                      control                                                                           control                                                        INGREDIENT 1   2   3  4  5  6  7  8  9  10                                    __________________________________________________________________________    ACRYLIC RESIN.sup.a                                                                      43.0                                                                              50.7                                                                              49.1                                                                             47.5                                                                             44.19                                                                            42.25                                                                            31.3                                                                             53.6                                                                             44.1                                                                             44.1                                  BLOCKED NCO.sup.b                                                                        22.8                                                                              26.8                                                                              28.2                                                                             29.6                                                                             32.3                                                                             33.95                                                                            25.5                                                                             37.3                                                                             32.3                                                                             32.2                                  AIR RELEASE                                                                              0.4 0.4 0.4                                                                              0.4                                                                              0.4                                                                              0.4                                                                              0.4                                                                              0.4                                                                              0.4                                                                              0.4                                   AGENT.sup.c                                                                   PLASTICIZER.sup.d                                                                        3.0 3.0 3.0                                                                              3.0                                                                              3.0                                                                              3.0                                                                              3.0                                                                              3.0                                                                              3.0                                                                              3.0                                   FLOW ADDITIVE                                                                            3.0.sup.e                                                                         3.0.sup.e                                                                         3.0.sup.e                                                                        3.0.sup.e                                                                        3.0.sup.e                                                                        3.0.sup.e                                                                        -- 1.5.sup.f                                                                        3.0                                                                              3.0                                   UV ABSORBER.sup.g                                                                        2.6 2.6 2.6                                                                              2.6                                                                              2.6                                                                              2.6                                                                              1.5                                                                              4.0                                                                              0.4                                                                              0.4                                   HALS.sup.h 1.4 1.4 1.4                                                                              1.4                                                                              1.4                                                                              1.4                                                                              2.6                                                                              2.2                                                                              2.6                                                                              2.6                                   LANCOWAX.sup.i                                                                           0.4 0.4 0.4                                                                              0.4                                                                              0.4                                                                              0.4                                                                              -- -- 1.4                                                                              1.4                                   WHITE PIGMENT                                                                            11.6                                                                              11.5                                                                              11.5                                                                             11.5                                                                             11.5                                                                             11.5                                                                             32.7                                                                             -- 11.5                                                                             11.5                                  BLACK PIGMENT                                                                            0.05                                                                              0.2 0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.6                                                                              -- 0.2                                                                              0.2                                   TMP.sup.j  --  --  0.25                                                                             0.5                                                                              1.0                                                                              1.3                                                                              1.0                                                                              1.0                                                                              -- --                                    NPG.sup.k  --  --  -- -- -- -- -- -- 1.0                                                                              --                                    CHDM.sup.l --  --  -- -- -- -- -- -- -- 1.0                                   FILLER.sup.m                                                                             11.75                                                                             --  -- -- -- -- -- -- -- --                                    __________________________________________________________________________     .sup.a Hydroxy functional acrylic resin.                                      .sup.b Caprolactam blocked isophorone diisocyanate.                           .sup.c Uraflow ® B, available from GCA Chemical, Bradenton, Florida       34205.                                                                        .sup.d Acid functional acrylic resin, available as SCX819, from S. C.         Johnson and Son, Racine, Wisconsin 53403.                                     .sup.e Amide modified polymeric ester sold under the trademark Powdermate     ®, available from Troy Corp., East Hanover, New Jersey 07936.             .sup.f A copolyacrylate sold under the trademark Perenol ® f30P,          available from Henkel Corp., Ambler, Pennsylvania 19002.                      .sup.g Tinuvin ® 900, uv light absorber, available from Ciba Geigy        Corp., Ardsley, New York 10502.                                               .sup.h Tinuvin ® 144, hindered amine light stabilizer, available from     Ciba Geigy Corp., Ardsley, New York 10502.                                    .sup.i Lancowax ® PPB62D, a paraffin wax, available from Cray Valley      Products, Stuyvesant, New York 12173.                                         .sup.j Trimethylolpropane                                                     .sup.k Baramite, a clay filler from Cyprus Foote Mineral Co., Malvern,        Pennsylvania 19335.                                                           .sup.l Neopentylglycol                                                        .sup.m Cyclohexyldimethylol                                              

EXAMPLES 11-14

Powder coating compositions are prepared from the ingredients set forthin Table 2 below. The powder coatings are prepared by premixing theingredients for 30-90 seconds, until homogenous. The premixed blend isthen extruded on a ZSK-30 (Werner Pfleider) twin screw extruder at thefollowing conditions.

Zone 1=130° C.

Zone 2=130° C.

RPM=250.

The flake is then re-extruded at the above conditions. The flake is thenground on an ACM-2L mill to 22-25 microns.

Coatings are applied with an ONODA spray gun, Model No. GX108. Panelsare sprayed with the powder coating composition to a thickness ofbetween 1.0 and 8 mils over electrocoated cold rolled steel (CRS). Thepanels are baked for 30 minutes at 350° F.

                  TABLE 2                                                         ______________________________________                                        Examples 11-14                                                                               Examples                                                       Ingredient       11     12       13   14                                      ______________________________________                                        ACRYLIC RESIN.sup.a                                                                            44.1   44.1     44.1 44.1                                    BLOCKED NCO.sup.b                                                                              32.2   32.2     32.2 32.2                                    AIR RELEASE AGENT.sup.c                                                                        0.4    0.4      0.4  0.4                                     PLASTICIZER.sup.d                                                                              3.0    3.0      3.0  3.0                                     FLOW ADDITIVE.sup.e                                                                            3.0    3.0      3.0  3.0                                     UV ABSORBER.sup.f                                                                              0.4    0.4      0.4  0.4                                     HALS.sup.g       2.6    2.6      2.6  2.6                                     LANCOWAX.sup.h   1.4    1.4      1.4  1.4                                     WHITE PIGMENT    11.5   11.5     11.5 11.5                                    BLACK PIGMENT    0.2    0.2      0.2  0.2                                     p-Cresol         1.0    --       --   --                                      2,4,6 Triphenylphenol                                                                          --     1.0      --   --                                      2,2'Biphenol     --     --       1.0  --                                      9-Phenanthrol    --     --       --   1.0                                     ______________________________________                                         .sup.a Hydroxy functional acrylic resin.                                      .sup.b Caprolactam blocked isophorone diisocyanate.                           .sup.c Uraflow ® B, available from GCA Chemical, Bradenton, Florida       34205.                                                                        .sup.d Acid functional acrylic resin, available as SCX819, from S. C.         Johnson and Son, Racine, Wisconsin 53403.                                     .sup.e Amide modified polymeric ester sold under the trademark Powdermate     ®, available from Troy Corp., East Hanover, New Jersey 07936.             .sup.f Tinuvin ® 900, uv light absorber, available from Ciba Geigy        Corp., Ardsley, New York 10502.                                               .sup.g Tinuvin ® 144, hindered amine light stabilizer, available from     Ciba Geigy Corp., Ardsley, New York 10502.                                    .sup.h Lancowax ® PPB62D, a paraffin wax, available from Cray Valley      Products, Stuyvesant, New York 12173.                                    

                  TABLE 3                                                         ______________________________________                                        Physical Properties of Cured Powder Films                                            PEEL @              GAS         SOLVENT                                EX-    2.0 MILS GRAVELO-   INVER- GAS  RESIS-                                 AMPLE  FILM     METER      SION   DIP  TANCE                                  ______________________________________                                        Control 1                                                                            7        7+         P           0                                      Control 2                                                                            8        7+         P           1                                      3      8        7+         P      P    1                                      4      8        7+         P      P    1                                      5      8/9      7+         P      P    1                                      6      8/9      7+         P      P    1                                      7      8        7+         P      P    0                                      9      8/9      --         P      P    0                                      10     8/9      --         P      P    0                                      ______________________________________                                    

We claim:
 1. A thermosetting powder coating composition comprising asolid particulate mixture ofa) a film-forming resinous binderincludingi) a copolymer selected from the group consisting of epoxy,polyester and acrylic copolymers having a reactive functionalityselected from the group consisting of epoxy, carboxy, and hydroxyfunctionalities and mixtures thereof and ii) a crosslinking agentcapable of reacting with the reactive functionality on copolymer (i)selected from the group consisting of aminoplasts, blocked aliphaticdiisocyanates, aromatic diisocyanates, acid anhydrides, dicyandiamideand its derivatives and mixtures thereof, b) a first flow control agentwhich is an aliphatic or aromatic hydroxyl containing crystallinecompound having a melting point between 30° C. and 150° C. and c) asecond, flow control agent different from the first flow control agent.2. The composition of claim 1, wherein the flow control agent (b) isselected from the group consisting of trimethylolpropane, neopentylglycol, (pentaerythritol), 2,5 dimethyl-2,5-hexanediol,2,4,6-triphenylphenol, 2, 2' biphenol, 9-phenanthrol and p-cresol. 3.The composition of claim 1, wherein the crystalline hydroxyl containingcompound (b) is present in an amount between 0.05 and 10.0 percent byweight based on total coating composition weight.
 4. The composition ofclaim 1, wherein the crystalline hydroxyl containing compound (b) ispresent in an amount between 0.25 and 5.0 percent by weight, based ontotal coating composition weight.
 5. The composition of claim 1, whereinthe film forming resinous binder includes copolymer (i) present in anamount between 90 and 10 percent by weight, and the crosslinking agent(ii) is present in an amount between 10 and 90 percent by weight, whereweights are based on the total weight of the resinous binder.
 6. Thecomposition of claim 1, wherein the film forming resinous binderincludes copolymer (i) present in an amount between 60 and 20 percent byweight, based on total coating composition weight and the crosslinkingagent (ii) is present in an amount between 20 and 50 percent by weight,based on the total coating composition weight.
 7. The composition ofclaim 1, wherein pigment is present in an amount up to 35 percent byweight.
 8. The composition of claim 1, further comprising additivesselected from the group consisting of pigments, anti-oxidants, curecatalysts, degassing agents and mixtures thereof, wherein the additivesand the flow control agent are present in an amount between 5.0 to 30.0%by weight.
 9. The composition of claim 1, wherein the copolymer (i) is ahydroxy functional acrylic copolymer.
 10. The composition of claim 9,wherein the crosslinking agent is selected from the group consisting ofaminoplast and blocked diisocyanate crosslinkers.
 11. A thermosettingpowder coating composition comprising a solid particulate mixture ofa) afilm-forming resinous binder includingi) a copolymer selected from thegroup consisting of epoxy, polyester and acrylic copolymers having areactive functionality selected from the group consisting of epoxy,carboxy, and hydroxy functionalities and mixtures thereof and ii) acrosslinking agent capable of reacting with the reactive functionalityon copolymer (i) selected from the group consisting of aminoplasts,blocked aliphatic diisocyanates, aromatic diisocyanates, and mixturesthereof, b) a first flow control agent which is an aliphatic or aromatichydroxyl containing crystalline compound having a melting point between30° C. and 150° C., selected from the group consisting oftrimethylolpropane, neopentyl glycol, (pentaerythritol), 2,5dimethyl-2,5-hexanediol, 2,4,6-triphenylphenol, 2, 2' biphenol,9-phenanthrol and p-cresol and c) a second, flow control agent,different from the first flow control agent.